The invention relates to a process as well as apparatus for the catalytic reaction of H.sub.2 S and S0.sub.2 to elementary sulfur, and especially to an improvement to a plant containing at least two catalyst beds, at least one of said catalyst beds being used for reaction of the sulfur compounds and adsorption of resultant sulfur and operated below the sulfur dew point, and at least one other catalyst bed being regenerated. In general, the resulting sulfur vapor obtained during regeneration is condensed by cooling.
In the processing of crude gas streams which contain sulfur in some form, a separation step is generally required to remove sulfur compounds, e.g., H.sub.2 S and S0.sub.2 ; otherwise, in most instances, the gas streams cannot be released into the environment or utilized commercially. Since many fossil fuels contain sulfur in bonded form, gas desulfurization is becoming increasingly important. The separation can be conducted in different ways, for example, adsorptively or catalytically or by physical or chemical scrubbing.
A suitable process is selected depending on the required degree of desulfurization and form of the conversion product of the sulfur.
A known process, in which H.sub.2 S and S0.sub.2 are converted to elementary sulfur, with a desulfurization efficiency of over 99% being assured, is, for example, a Claus process with four serially connected catalytic reactors, with the last two being operated below the sulfur dew point. As a consequence, the chemical equilibrium is shifted more strongly in the direction of reaction of H.sub.2 S and S0.sub.2 to elementary sulfur than in a conventional Claus process in which temperatures are not permitted to fall below the sulfur dew point in any of the catalytic reactors.
The reason for this is that a major part of the formed sulfur is removed from the stream by adsorption on the catalyst and thus the equilibrium of the reaction EQU 2 H.sub.2 S+S0.sub.2 .fwdarw.3/x S.sub.x +2 H.sub.2 O +.DELTA.H
is shifted by the sulfur elimination to the right side of the equation.
The catalyst is inactivated by the sulfur condensation so that it must be regenerated after a certain time. To maintain a continuous operation of the plant, of the four reactors the first is always operated as a conventional Claus reactor, one is regenerated, while the other two are run below the sulfur dew point. For regeneration, the gas stream, for example, is heated up by means of gas-gas heat exchangers so that by passing the heated gas over the catalyst loaded with sulfur, the sulfur is evaporated.
If the sulfur loading of the catalyst reaches a certain level, an automatic switching of the reactor to the regeneration phase and a corresponding switching of the two reactors working below the sulfur dew point take place.
Such a process is described, for example, in Oil & Gas Journal of Sept. 12, 1983, on pages 156-160.
The known process has the great cost disadvantage that at least four Claus reactors, of which two in each case are operated below the S dew point, are necessary to achieve an S recovery of over 99%. (Conversely, when fewer than four Claus reactors are used in other processes, additional measures must be taken, for example, SO.sub.2 recycling, in order to meet increasingly stringent emission requirements.) Moreover, the known process has the further disadvantage that many valves and pipes are necessary for operation of the plant with on-line regeneration. In this connection, problems occur, especially with the valves caused by corrosion and faulty sealing (they must be gas-tight). Moreover, it is necessary to heat the valves so that the sulfur, which is contained in the gas stream, will not condense out. Further, even very slight impurities of the gas stream with solid particles, such as, for example, dust, can result in the loss of sealing of the valves.
Since the gas stream from the conventional Claus reactor usually is under a very low pressure, the gas stream has a correspondingly large volume, which, in turn, requires correspondingly large valves.
Thus, there result high wear costs, high assembly expenditures, high proneness to failure and a large space requirement for the plant. These factors lead, on the whole, to relatively high investment and operating costs.